Oohh boy. Looks like I might have a 1/2" problem (don't know why I didn't think about this before...).

Is there usually an allowance in this 12" standard or is 12" the absolute minimum?

: They are referring to the measurement from the finished wall, whether that is drywall or tile.

: : Just to clarify...

: : When everyone talks about a 12" rough-in for a toilet drain, are we talking about 12" from the centre of the drain to the studs, or to the finished wall (i.e. drywall). I know it's only 1/2" or so, but that could make all the difference...